Direct fired burner



Dec. 2, 1969 H. M. KOHN 3,481,680

DIRECT FIRED'BURNER Filed Nov. 20, 1967 INVENTOR.

f/aeaser M. Aa/m/ United States Patent 3,481,680 DIRECT FIRED BURNERHerbert M. Kohn, Toledo, Ohio, assignor to Midland- Ross Corporation,Toledo, Ohio, a corporation of Ohio Filed Nov. 20, 1967, Ser. No.684,319 Int. Cl. F23m 1/00, 4/00; F23d 15/00 US. Cl. 431-182 3 ClaimsABSTRACT OF THE DISCLOSURE This invention relates to a direct firedburner that provides a flame capable of spreading across the surface ofa furnace wall. The burner is attached to a wall about, and coaxiallywith, an opening within the wall that defines a combustion chamber. Theburner has a first cylindrical member defining a passageway that isconfluent with the combustion chamber and into which fuel is introducedaxially. Air -is introduced into this passageway tangentially to imparta stable flame thereto. Disposed about the first cylindrical member is asecond cylindrical member forming an annular plenum therebetween intowhich air is introduced tangentially. The plenum is in confluentrelationship with the combustion chamber and air flows therefrom intothe combustion chamber with a spinning act-ion. When air from the plenummeets the ignited fuel emerging from the passageway at the entrance ofthe combustion chamber, the airfuel mixture tends to hug the walls ofthe combustion chamber as they emerge therefrom due to the effect of thespinning gas flows.

In heat treating operations, it is often desirable to uniformly disperseflame from a burner so that heat may be extended over a large surfacearea. By so doing, a large quantity of heat may be applied without toogreat an amount of heat being concentrated in one area, thus tending toeliminate damaging high temperatures. An example of applications where aspreading flame is desirable is the heat treating of metal sheets incoil annealing furnaces. One way that heat has been provided over alarge area in the past is to fire burners through the furnace end wallsinto radiant elements located along the length of the furnace. Thismethod does not give the degree of flexibility in controlling orchanging the heat pattern along the furnace length that is needed.Also,the radiant elements are expensive and have to be periodicallyreplaced because of bum-out problems. This involves considerablemaintenance and furnace down time. Consequently, it would be beneficialto have a small number of burners capable of providing relative uniformheat across a large expanse.

It is, therefore, an object of this invention to provide a burnercapable of spreading a flame across a large area.

It is another object of this invention to provide a furnace with aburner having spinning gas streams that spread the flame issuingtherefrom across a large surface of the furnace.

It is still another object of this invention to provide means forradiantly heating work using a combustion burner.

It is a further object of this invention to provide a burner thatrequires no premix pilot and yields a spreading flame at a lower airpressure drop.

In the drawings:

FIG. 1 shows a cross sectional, elevational view of a burnerencompassing the features of the instant invention.

FIG. 2 is a view taken along the lines 22 of FIG. 1.

Referring now to the drawing, a burner is shown generally at andincludes part of a furnace wall 12 having an opening 14 therein.Refractory material 16 is received within the opening 14 and defines acylindrical combustion chamber 17. The refractory material 16 has acurved surface 18 formed at one end thereof adjacent the inner surface19 of the furnace wall 12. An annular orifice plate 20 is secured to therefractory material 16, as by bolts 22, about the chamber 17. The bolts22 are received by a collar 23 that is welded to the furnace wall 12.Secured to the orifice plate 20 is a first cylindrical member 24 that isdisposed coaxially with the combustion chamber 17. Received within thecylindrical member 24 is a second cylindrical member 28 that forms aplenum 29 between the two cylinders. The second cylindrical memberdefines a passageway 31. The diameter of the first member 24 is largerthan the diameter of the combustion chamber 17 and the diameter of thesecond member is smaller, thereby defining a shoulder 33. Between thesecond cylindrical member 28 and the shoulder 33 an orifice is formedthat provides a confluent relationship between the plenum 29 and thecombustion chamber 17.

Secured to the back end of the first and second cylindrical members 24and 28 is an annular back plate 30 having a central opening 32 therein.The back plate 30 partially encloses the plenum 29 and passageway 31. Afuel pipe 34 is received within the central opening 32 and is coaxialwith the passageway 31. A plate 36 having a central opening 38 issecured to the inside end of the fuel pipe 34.

The first cylindrical member 24 has an opening 40 therein that receivesa generally radially extending air pipe 42. The air pipe 42 has aconverging portion 44 that directs air tangentially into the plenum 29at a slight positive pressure. The second cylindrical member 28 has aplurality of circumferentially disposed radial apertures 46 therein sothat a portion of the air received within the plenum 29 flows radiallyinto the passageway 31. At the upstream end of the annular member 28, apair of tangential air inlets 50 is secured within the walls of themember to provide a supply of spinning air to the passageway 31, the airflowing through the inlet pipes 50 from the plenum 29.

The back plate 30 has a second opening 52 therein, which openingreceives a spark plug 54. The spark plug 54 serves to ignite the fuelsupplied from the pipe 34 and air coming from the tangential air inlet50, only a small percentage of the total air required for combustionbeing provided by the tangential air inlet pipes. A spinning air streamis thus formed that circumposes the axially flowing fuel stream emittedinto the passageway through the fuel pipe 34. The combustible mixture offuel and air formed at the interface of the spinning air stream and theaxially flowing fuel stream is ignited by the spark plug 54 to establisha spinning, slow mixing, stable flame. The air entering apertures 46produces a back eddy current that promotes stable burning with maximummixing.

The air directed into the plenum 29 from the air pipe 42 spins withinthe plenum as a result of the converging portion 44. The spin imparts acentrifugal force to the air, which force causes the bulk of the air toflow in close proximity to the cylindrical member 24, which is the outerwall of the plenum 29. As the air thus spins, it tends to form a helix,while traveling along the plenum 29. If the air were to enter thecombustion chamber 17 with a helical pattern, it would create acondition of fluctuating temperature resulting from non-uniformcombustion. To eliminate this problem, a restriction, in the form of theshoulder 33, is provided that causes a pressure drop as the air flowsthrough the orifice 35.

It has been found advantageous to have the restricting member, shoulder33, adjacent the outside wall of the plenum 29 so that the air flowsinto the chamber 17 along the second cylindrical member 28, or insidewall of the plenum 29. It has been found that a much higher pressuredrop is required to disrupt the helical pattern when the orifice 35 islocated adjacent the outside wall of the plenum 29. The reason for thisis believed to be that the shoulder 33 causes the spinning air that istraveling along the outside wall of plenum 29, due to the centrifugalforce, to turn at a right angle before it enters the chamber 17 when theshoulder 33 is adjacent the outside wall of the plenum. This abrupt turntends to break up, or distort, the helical pattern, and thus requires areduced pressure drop than if the orifice 35 were located adjacent theoutside wall of plenum 29.

As the air spins along the length of the plenum 29, it enters thecombustion chamber 17 through the orifice 35 located between the secondcylindrical member 28 and the shoulder 33. This combination forms a venacontracta that will tend to cause the resulting mixture of fuel and airto expanded as it enters the combustion chamber 17. This expansion andthe effect of the spinning gases tend to keep the flame close to thewall of the combustion chamber 17. As the air and fuel mixture passesthrough the combustion chamber 17 and across the curved portion 18, thetendency to keep on the wall continues beyond the curved portion so thatthe exiting flame tends to cling to the furnace wall inner surface 19.

The burner shown and described has two distinct advantages over priorburners in that no premix pilots are required and the spreading flame isobtained at a lower air pressure drop. The need for a premix pilot isobviated by the presence of the spinning air stream that is provided bythe tangential air inlets 50. This air stream yields a stable flameafter initial ignition by the spark plug 54.

In the prior practice, spinning air is achieved by a pressure dropacross specifically shaped orifice plates, for example, half moon shapedopenings. The need for such specifically shaped orifices is eliminatedin the burner of this invention because the air is introducedtangentially by the conveying portion 44 of the air pipe 42. Thisspinning air, along with the location of the orifice 35 as previouslydescribed, reduces the air pressure requirements.

Thus, a burner having high capacity can be provided to yield a largequantity of heat over a substantial area so that a large quantity ofheat may be provided to the work being heat treated without raising thetemperature of the work to a point where damage would result therefrom.The heat supplied to the work is in the form of radiant heat for theflame heats the refractory wall, which in turn radiantly heats the Work.With the burner 10, there is no direct impingement of the flame upon thework; consequently, no discoloration or other damaging effects areimparted to the work.

Although only a single embodiment of this invention has been shown anddescribed, it is understood that changes and modifications can be madetherein, and this description is illustrative only and not for thepurpose of rendering this invention limited to the details illustratedor described except insofar as they are limited by the terms of thefollowing claims.

I claim:

1. In an industrial gas burner, a wall member defining a combustionchamber having spaced, open ends, a housing having a first rightcylindrical member, means for securing said first cylindrical membersubstantially normally to one end of said wall member in coaxialalignment with said chamber, a second cylindrical member coaxiallydisposed within said first member to define a plenum therebetween, saidplenum being confluent with said combustion chamber, said firstcylindrical member having a larger diameter than said combustion chamberand said second cylindrical member having a smaller diameter than saidcombustion chamber, thereby defining a restriction means where saidplenum and said combustion chamber are confluent, means for supplyingfuel axially to said second member, means for supplying air tangentiallyto said second member, and means for supplying air tangentially to saidplenum.

2. The burner of claim 1 wherein the end of the combustion chamberopposed to the housing has outwardly curved surfaces.

3. In an industrial burner, the combination comprising: a furnace wallhaving a cylindrical opening therein, a right cylindrical housing, meansfor securing said housing substantially normally to a first side of saidfurnace wall coaxially with the opening, said housing having a largerdiameter than the opening, thereby defining a shoulder about theopening, a cylindrical sleeve received within said housing and having adiameter smaller than the opening to form an orifice in cooperation withthe shoulder, said housing and said sleeve defining a plenumtherebetween, means for supplying air tangentially to said plenum, meansfor supplying a combustible fuel to said sleeve, means for introducingair tangentially to said sleeve, and means for igniting the air-fuelmixture in said sleeve.

References Cited UNITED STATES PATENTS 2,952,307 9/1960 Schramm et al 43l18 3,187,799 6/1965 Nesbitt 431-9 3,267,984 8/1966 Reed et al 431EDWARD G. FAVORS, Primary Examiner

